Apparatus for controlling charging of storage batteries with sensing the d.c. of the electrolyte

ABSTRACT

My invention relates to a device for the testing or analyzing of batteries to determine whether such is chargeable or unchargeable, and more particularly, it relates to an electronic sensing system for automatically conducting and providing a readout display which is instantly indicative of the state of a given battery with respect to its chargeability.

United States Patent 1 Seabase Jan. 22, 1974 Assignee:

APPARATUS FOR CONTROLLING CHARGING OF STORAGE BATTERIES WITH SENSING THEI).C. OF THE ELECTROLYTE Paul L. Seabase, Sterling Heights, Mich.

The United States of America as represented by the Secretary of theArmy, Washington, DC.

Filed: Aug. 16, 1 972 Appl.-No.: 281,082

Inventor:

us. Cl. 320/43, 324/29 Int. Cl. H02j 7/04 Field of Search... 324/29,29.5, 61; 331/65, 40;

References Cited UNITED STATES PATENTS 6/1947 Odessey 331/65 X 3,646,5412/1972 Rathbun 331/65 X FOREIGN PATENTS OR APPLICATIONS 1,125,044 9/1959Germany 320/43 Primary Examiner-J. D. Miller Assistant Examiner-RobertJ. Hickey Attorney, Agent, or FirmEdward J. Kelly; Herbert Berl; R. M.Lyon [57] ABSTRACT My invention relates to a device for the testing oranalyzing of batteries to determine whether such is chargeable orunchargeable, and more particularly, it relates to an electronic sensingsystem for automatically conducting and providing a readout displaywhich is instantly indicative of the state of a given battery withrespect to its chargeability.

6 Claims, 1 Drawing Figure CHARGER 45 APPARATUS FOR CONTROLLING CHARGINGOF STORAGE BATTERIES WITH SENSING THE D.C. OF THE ELECTROLYTE Theinvention described herein may be manufactured, used, and licensed by orfor the Government for governmental purposes without payment to me ofany royalty thereon.

BACKGROUND OF THE INVENTION Field of the Invention In present vehicularapplication a charging source, generator or alternator-rectifier,impresses electrical energy to the storage battery. This energy flow,characterized by the current rate, is controlled by an electromechanicalsystem which senses the battery voltage. This voltage. regulator turnson the charging source, when the batteryvoltage drops below a specificvalue, and turns it off again when the voltage rises to a specificmaximum. During the charging period the current rate is almost constantand it is not in accordance with the receptivity of the battery.

This invention relates to the change of frequency of a variablefrequency oscillator which frequency change is brought about by thecapacity variation of a capacitive sensor. The capacity variation ofthis sensor is caused by the change of the dielectric constant of thebattery electrolyte which change is proportional to the state of chargelevel in the battery.

This invention seeks to avoid overcharging which is specificallyunfavorable when in the cycling of the vehicles battery a short highload period is followed by a relatively long charging period. The excessenergy resulting from the overcharging produces excessive heat in thebattery and unnecessary gas is formed by the electrolytic dissociationof the water present in the electrolyte. Overcharging does not directlycause the battery to fail prematurely but it contributes to its fasteraging. It in effect shortens the cycling life by abnormally increasingthe natural decay of the active electrode material.

In vehicular application the discharging halfcycle is uncontrollablebecause of the multitude of load components. It is utterly unpredictablewhen and how much load will be turned on and for how long and how often.Only the charging halfcycle allows any control.

Prior Art A batterys state of charge testing program exists whichcomprises a series of closely timed alternating discharging and chargingsteps by which the chargeability of a battery could be determined withacceptable accuracy.

Devices for carrying out these methods have not been completelysatisfactory because they depend on the operator to manually instituteat least some of the charging and discharging steps in the test process.Accuratesequence timing of these steps is of utmost importance. Humanerrors have been quite common in the use of such prior art devices tothe extent that the results obtained have had questionable values. Thereadout techniques utilized in such prior relatively unsophisticateddevices have not had the desired combination of simplicity andexactness, so that a typical operator possessing only ordinary skillswas susceptible to errors in reading his results.

It has already been proposed to use polar liquids of high purity as thedielectric medium in various apparatus exposed to intense electricfields.

Purified polar liquids have been found initially to possess very highdielectric properties unparalleled by most other categories ofsubstances. As a drawback, however, it has been found that these highinitial characteristics are not maintained but decrease sharply duringthe activation of the apparatus due to contamination of the liquid fromvarious sources. Minute amounts of contaminant, such as smallconcentrations of material dissolved away from the wall surfaces of thevessels storing the liquids, are sufficient to cause a sharp drop in thedielectric properties of the liquid and conse-" quently destroy theoverall advantages expected from the use of polar liquids.

Prior attempts in overcoming the difficulty, by providing means forcontinually purifying the dielectric liquid during operation of themedia in which it is used, consisted of providing means for a continuouscirculation of the liquid through a closed flow circuit which comprisesthe apparatus and purifying means exterior to the apparatus. Circulatormeans were provided for continuously cycling the solution around thecircuit so as to feed purified liquid into the apparatus. Such meanshave been found quite satisfactory in many cases where system dimensionsand complexity do not constitute limiting factors. This method has madepossible the continued pressure, within the electric field of theapparatus, of a pure polar liquid having resistivity and dielectriccharacteristics of values heretofore unattainable by other means. Anarrangement of such type is entirely unsuitable in a great manyapplications and it wouldbe extremely difficult to achieve the highdielectric values of polar liquids in a permanent manner throughout theservice life of the apparatus involved, without providing thecomplicated equipment comprising the fluid circulating and purifyingmeans as well as the excess body of liquid inherently present in such aset up.

The presently used conventional method of measuring the state of chargeof lead-acid storage batteries consists of checking the specific gravityof the electrolyte with a hydrometer. The latter method has severalshortcomings which reduce the accuracy of the measurement as well asreducing the practical application of it in the automotive field.

The hydrometer method cannot be used on vehicles which are in motion. Itcan only be utilized while the vehicle is completely immobilized and thebattery at rest. The method can only be used for making spot checks andis impractical for continuous monitoring of the storage batterys stateof charge. Further, the hydrometer readings are affected by temperaturesince a change of temperature causes a change in the electrolytesdensity.

Another method which offers a partial solution for the measurement ofthe state of charge in storage batteries is the resonance method.

SUMMARY OF THE INVENTION In the process which occurs through the cyclingof a lead-acid storage battery simultaneous electrical andelectro-chemical phenomena are involved. It is not possible to directlyexpress the state of charge of a leadacid storage battery by an explicitmathematical relation. In the development of a regulated charging systemknowledge of the state of charge of the system is necessary. Acontrolled charging system can be developed if the state of charge maybeaccurately determined.

The direct measurement of small capacity differences is complicated anddifficult to perform. Unavoidable component capacitances make themeasurements uncertain. When the sensor capacity is incorporated as acapacitive component into a high frequency oscillatory system, thecapacity variation of the sensor causes a variation in the oscillatorsfrequency. This frequency variation is easier to handle. In the systemthe unaccountable stray capacitances can be compensated or cancelled outautomatically.

if the reference frequency of the oscillator is set at the referencecondition of the battery (full charge or normal discharge state), thefrequency variation ensuing during the batterys cycling is proportionalto the variation of the state of charge.

The measurement of high frequencies is not simple and requires specificand sophisticated equipment. It is feasible only for closely controlledlaboratory conditions. Such method which offers a complete solution tothe practical and accurate measurement of the state of charge of alead-acid battery is the basis of my invention.

The method incorporates two oscillators instead of one. One is thereference oscillator and is a fixed frequency crystal controlled system.The second oscillator is a variable frequency oscillator (VFO). This VFOcontains in its circuit capacity, as a component, the capacitive sensor.in its circuit, the only other variable capacity component is a smalltrimmer used for alignment to reference. At normal'discharge statealigning the variable frequency oscillator with the crystal oscillatorfeeds the output into a mixer stage. When the frequency of bothoscillators is equal then the output of the mixer will be zero beat. Theindication of reference alignment is zero output from the mixer.

The electrolyte of a typical and common lead-acid storage battery isdiluted sulphuric acid (H 80 having a specific gravity of 1.280. Whenthe battery is being discharged, by the electrochemical reaction, aspecific amount of H 80 is converted to lead sulfate (PbSO and water (HO) which is likewise a by-product of this reaction. During thisreversible process the specific gravity of the electrolyte decreases toapproximately 1.220.

in the opposite charging process PbSO, molecules in the electrodes areelectrolytically broken down and the sulfate ion (80f) recombines withhydrogen (H from the water while free oxygen and hydrogen (H aregenerated as by-products and escape from the electrolyte.

The molecular ratio of the electrolytes two components alwayscorresponds to an actual and specific state of charge and this is alwaysindependent of the temperatures influence. The electrolyte has aspecific dielectric constant which depends only on the molecular ratioof the component ingredient namely aqueous sulphuric acid. When themolecular ratio of the sulphuric acid and water changes proportionatelywith the state of charge, then the dielectric constant also changes inthe same proportion. By increasing the sulphuric acids concentration thedielectric constant is decreased. The latter occurs during charging. Thedielectric constant increases with decreasing concentration of sulphuricacid which occurs when the battery is discharging.

It is possible to measure the dielectric constant of the batteryselectrolyte directly, which measurement shall be an indication of itscorresponding state of charge. Indirectly this measurement may beperformed by simple means, namely measuring the capacity variation of acapacitor sensor in which the dielectric constant of the particularelectrolyteis the only variable magnitude.

Because the battery's electrolyte is an electrically conductive materialthe armatures of the sensor capacitor must be separated from each other.To accomplish this separation an insulating layer is sufficient on oneof the armatures. Although the capacity of the sensor will be determinedby a combined dielectric constant, its capacity variations will occuronly as a result of the variations of the dielectric constant of theelectrolyte. Such capacitive sensor can be applied on the batterywithout disturbing its stru'cturalintegrity. The outermost negativeelectrode at the negative battery terminal is engaged as one armature ofthe sensor while the other armature may be a metal plateadherent to theoutside of the container and opposite to the negative electrode adjacentto the container wall. The dielectric sensor will be located between thenegative electrode and the container wall close to the electrolyte.

The contact area of the thus formed sensor capacitor is determined bythe overall dimensions of the armature plate which must be slightlysmaller than its opposite armature, the negative electrode.

All of the well known methods and arrangements available in the art,including the resonance method, allow quite accurate measurements butare practical for laboratory use only. These methods require manualresetting of the resonance and complicated charging system control.

It is an object of the present invention to provide a simplifiedapparatus and method for the automatic testing of the state of charge ofa lead-acid storage battery.

It is another object of the present invention to provide an apparatuswhich will indicate the state of charge of a lead-acid storage batteryat any time, whether the battery is in the operating or resting stage.

It is yet an object of my invention to provide a battery charge testerwhich senses the variation of the dielectric constant of the storagebatterys electrolyte.

It is still another object of the instant invention to provide a novelmethod and apparatus for indicating the state of charge of storagebatteries which is controlled automatically according to the inherentcharging characteristics of the storage battery.

It is also another object of the instant invention to provide anapparatus possessing a high dielectric constant which will greatlyimprove operating characteristics over comparable apparatus ofconventional character.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being made to the accompanyingdrawing which shows the charger apparatus and method disclosed herein.

BRIEF DESCRIPTlON OF THE DRAWING The accompanying drawing is a blockdiagram of the beat frequency method, closed loop system, embodying oneexample of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT When a battery 2 is beingcharged the dielectric constant of its electrolyte 3 will decreaseproportionally with the progress of the charging, namely with thebuild-up of the state of charge. As a result there is a decrease in thecapacity of sensor.4, comprised of outside armature 5 and negativeelectrode 6, and consequently the frequency of the variable frequencyoscillator (VFO) 7 will shift upwards thus becoming largerthan thefrequency of crystal oscillator 8. The output of mixer is the differencebetween the two inputoscillators 7 and 8 which is an actual beatfrequency. This beat frequency will increase when the state of charge isincreased. The range of the beat frequency output can vary from 0 to10,000 audio frequency. This audio frequency signal is fed into a systemwhich by direct readout indicates the state of charge. It may also beused as a signal for triggering the charger regulating system whichadjusts the charging current corresponding to the state of charge to thecorrelated receptivity of the battery.

The two oscillators 7 and 8 together with the mixer 10 stage incorporatea beat frequency oscillator. Regulator 9 which effects the control ofthe current is a separate system incorporated to the beat frequencyoscillator.

At reference condition variable frequency oscillator 8 is aligned with avariable capacity component of the circuit capacity to resonance withthe crystal frequency. At this point the output of the mixer stage iszero beat. It is preferred to take the normal discharge state asreference condition.

When the charging begins the dielectric constant of electrolyte 3 andthe capacity of sensor 4 will change. The dielectric constant ofelectrolyte 3 will decrease as will the capacity of sensor 4. The outputof mixer 10 is the difference between the two frequencies, namely thebeat frequency and the variable frequency. The frequency of the variablefrequency oscillator is larger than that of the reference. The notedfrequency difference increases with the build-up progress of the stateof charge.

The small change in the dielectric constant causes a similarly slightchange in sensor 4 capacity wherein the output of the beat frequency ofthe system will be in the range of audio frequencies. The system can beso designed that the range of the beat frequency oscillator output shallrange from 0 to IO QQO audio frequencies. The frequency signal from thebeat frequency oscillator (BFO) system is used as an input to a visualreadout system as well as an input for a current regulating system.

The audio frequency output of the BFO is proportional to the state ofcharge as the variation of the dielectric constant of sensor 4 capacity.As a result specific beat frequencies are correlated to specific pointsof the state of charge function. The quoted points will be points atwhich the current should be decreased for regulated charging; thecorrelated beat frequencies may be utilized to trigger the regulatingsystem.

The input of regulator 9 must have as many narrow bandpass filters asthere are triggerpoints. It is then that these filters will pass onlythe specific trigger frequencies to a switching system. This two waycontrol of the charging current makes it virtually impossible for thebatterys discharge to go beyond an allowable limit. It will limit thecurrent rate approximately to the receptivity and thus greatly reducethe development of heat and electrolytic dissolution losses which arethe normal consequences of a constant current charging.

The audiofrequency output of the BFO is proportional to the state ofcharge. This signal is impressed into direct reading audiofrequencymeter 11 wherein the instrument can be calibrated directly in terms ofstate of charge.

Such visual readout is important in vehicles wherein the actual value ofthe state of charge is necessary with respect to cranking capability ofthe engine. The lowest state of charge, at which a full start ispossible, could even be red-marked on visual readout scale 11.

Indirectly the visual readout may also be used to judge the aging of thebattery or monitoring its condition. Aging would be readily noticeableby a gradual decrease of the maximum state of charge at completedcharging and the condition of the battery could be monitoredquantitatively. An impending or beginning cell failure would show up asan inadequate state of charge after a prolonged charging. A slowcreeping decrease of the state of charge during idle periods wouldchange to a more rapid rate which is mainly due to internal leakage.Additionally visual readout of the state of charge would also beimportant and desirable for a periodic maintenance check.

The entire system is transistorized and the relatively negligiblecurrent drain makes it possible to operate the instrument from aself-contained battery. In vehicular applications it is preferred to usethe vehicles battery itself as a power source.

The VFO of the monitoring system is very sensitive to the variation ofthe driving voltage, consequently it is desirable to secure a steadydriving voltage for it in vehicles. This can be achieved when the powertakeoff from the vehicular battery occurs by a Zener diode which limitsthe voltage lower than the cutoff voltage of the regulator. Thepreferred limit is 9 volts.

The reference capacity of sensor 4 must be relatively large because thevariation of the dielectric constant of electrolyte is subtle betweennormal discharge and full charge state. Keeping sensor 4 capacity largeenough, a measurable capacity variation is obtained by the variation ofthe electrolyte's dielectric constant.

I wish it to be understood that I do not desire to be limited to theexact details of description shown and since various changes andmodifications may be made in the invention without departing from thespirit and scope of the invention as described hereinabove and asdefined in the following claims.

I claim:

1. In combination: a battery of the wet cell type; a charging source forthe battery; an armature capacitively coupled to a plate of the batterythrough the battery electrolyte means coupled therewith for generating avariable frequency signal representative of the electrolytes dielectricconstant; a regulator means for limiting the the current delivered fromthe charging source to the battery; and means responsive to the variablefrequency signal for automatically adjusting and changing the currentlimit setting of the regulator means so that throughout the charge cyclethe charging current is set at values which are inversely proportionalto the dielectric constant of the electrolyte.

2. The combination of claim 1 wherein the frequency-responsive adjustingmeans comprises a beat frequency oscillator system.

3. The combination of claim 2 wherein the beat frequency oscillatorsystem comprises a fixed frequency reference oscillator powered by theaforementioned battery.

4. The combination of claim 1 wherein the frequency-responsive adjustingmeans comprises a beat frequency oscillator system containing a firstfixed frequency reference oscillator and a second variable frequencyoscillator, said second oscillator being powered by the aforementionedvariable frequency signal; said first and second oscillatorsbeinginterconnected so that the output of the oscillator systemrepresents the frequency difference of the two oscillator outputs.

5. The combination of claim 4 wherein the oscillator system is adjustedso that the beat frequency output is zero when the battery is in thedischarged state.

6. The combination of claim 1 wherein the regulator means includes aninput having a plurality of different narrow bandpass filters, eachcapable of passing a different frequency signal received from theaforementioned adjusting means; said regulator means including an outputwhich comprises a switching system triggered by the input signals sothat the battery charging current is relatively large when the batteryapproaches the discharged state and relatively small when the batterynears the charged state.

1. In combination: a battery of the wet cell type; a charging source forthe battery; an armature capacitively coupled to a plate of the batterythrough the battery electrolyte means coupled therewith for generating avariable frequency signal representative of the electrolyte''sdielectric constant; a regulator means for limiting the the currentdelivered from the charging source to the battery; and means responsiveto the variable frequency signal for automatically adjusting andchanging the current limit setting of the regulator means so thatthroughout the charge cycle the charging current is set at values whichare inversely proportional to the dielectric constant of theelectrolyte.
 2. The combination of claim 1 wherein thefrequency-responsive adjusting means comprises a beat frequencyoscillator system.
 3. The combination of claim 2 wherein the beatfrequency oscillator system comprises a fixed frequency referenceoscillator powered by the aforementioned battery.
 4. The combination ofclaim 1 wherein the frequency-responsive adjusting means comprises abeat frequency oscillator system containing a first fixed frequencyreference oscillator and a second variable frequency oscillator, saidsecond oscillator being powered by the aforementioned variable frequencysignal; said first and second oscillators being interconnected so thatthe output of the oscillator system represents the frequency differenceof the two oscillator outputs.
 5. The combination of claim 4 wherein theoscillator system is adjusted so that the beat frequency output is zerowhen the battery is in the discharged state.
 6. The combination of claim1 wherein the regulator means includes an input having a plurality ofdifferent narrow bandpass filters, each capable of passing a differentfrequency signal received from the aforementioned adjusting means; saidregulator means including an output which comprises a switching systemtriggered by the input signals so that the battery charging current isrelatively large when the battery approaches the discharged state andrelatively small when the battery nears the charged state.